<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1">
    <!--Scripts-->
    <script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script>
    <script src="http://maxcdn.bootstrapcdn.com/bootstrap/3.2.0/js/bootstrap.min.js"></script>
    <!--Stylesheets-->
    <link rel="stylesheet" href="http://maxcdn.bootstrapcdn.com/bootstrap/3.2.0/css/bootstrap.min.css">
    <link rel="stylesheet" href="//maxcdn.bootstrapcdn.com/font-awesome/4.3.0/css/font-awesome.min.css">
    <title>Doc</title>
</head>
<body>

<div class="container-fluid centerDisp">
    <form class="blockDisp" name="productform" method="post" action="payment.php">
        <div class="blockDisp">
            <div class="forminputdiv blockDisp">
                <label class="fw-120 label-1">Product name</label>
                <input class="medInput" type="text" name="product">
            </div>
            <div class="forminputdiv blockDisp">
                <label class="label-1 fw-120">Quantity</label>
                <input class="medInput" type="number" step="any" min="0" max="15" name="quantity">
                <!--                <input class="medInput" type="string" name="quantity">-->
            </div>
            <div class="forminputdiv blockDisp">
                <label class="label-1 fw-120">price</label>
                <select class="medInput" type="number" name="price">
                    <option value="5.00">5.00</option>
                    <option value="8.00">8.00</option>
                    <option value="12.00">12.00</option>
                    <option value="18.00">18.00</option>
                    <option value="25.00">25.00</option>
                    <option value="60.00">60.00</option>
                </select>
            </div>
            <br>
            <div class="forminputdiv flex-middle">
                <button class="submission fw-200" value="submit">Submit</button>
            </div>
        </div>
    </form>
</div>
<script>

    $('input[name="quantity"]').on('change', function(){
        var thisval = $(this).val();
        $(this).val(thisval + '.00');
    });

</script>

</body>
</html>